The present invention relates to heat-sinking arrangement for circuit elements, e.g., central processing units (CPU) incorporated in information apparatuses, specially portable computer terminals, which elements require sinking heat produced by them.
A CPU and other electronic components mounted on a printed substrate should be surely protected from being self heated in working state to assure normal operation of them. Many kinds of protections have been proposed and applied.
FIG. 1 shows an exemplified cooling arrangement for a CPU used in a universal type desk-top personal computer. In the shown construction, a cooling fan 33 is directly attached to the top of the CPU 32 mounted on a substrate 31. Namely, the CPU 32 is forcibly cooled by the cooling fan 33. In FIG. 6, numeral 34 designates a lead wire of the CPU 32.
FIG. 2 shows an exemplified cooling arrangement for a CPU used in a portable type personal computer that has no space for mounting a cooling fan for cooling the CPU. Therefore, the CPU 32 mounted on a substrate is provided at its top with and a cushion 36 made of electrically insulating and thermally conducting material and a radiation metal plate 35 for transferring heat from the CPU 32.
FIG. 3 shows another exemplified cooling arrangement for a CPU used in a further compact portable type personal computer. The computer has further restricted spacing above the CPU in a housing. Therefore, the multilayer substrate 37 on which the CPU is mounted is used for radiating heat from the CPU 32.
Namely, the multilayer substrate 37 has a cavity 39 that extends to an earthing copper layer formed in the depth thereof and is filled with, e.g., silver paste 40 or a copper-made spacer. The CPU 32 is mounted on the thus prepared seat of the substrate. The CPU can now be in contact with the earthing layer 38 through which heat radiation from the CPU is dissipated. In FIG. 3, numeral 41 designates an insulating layer of the substrate.
However, the arrangement shown in FIG. 3 for dissipating heat away from the CPU through the earthing copper layer 38 formed in the depth of the substrate 37 has a small heat-transfer effect and can not sufficiently dissipate heat away from the CPU through the substrate.
The arrangements shown in FIGS. 1 and 2 are excellent to cool the CPU or dissipate heat away from the CPU but cannot be applied in a miniature type computer smaller than the portable type because the former has no space for accommodating the fan 33 or the heat-radiation plate. The arrangements of FIGS. 1 and 2 are designed to improve the effect of transferring heat from the CPU mounted on a substrate by providing a large space around the CPU in the housing.